250 ANTIMONY AND ITS ALLOYS 5. Determination of the Arsenic.—See Copper. * * * Hard lead contains variable quantities of antimony (usually 10-25%) and may contain small amounts of copper, tin, iron, nickel, arsenic, etc. The following table contains the results of analysis of samples of hard lead obtained directly, from ores of lead and antimony (Schnabel) : TABLE XXX Composition of Hard Leads i on OberharzJlI . . [ill. . . Freiberg . | 81-71 . i 82-44 . : 82-08 • 17-69 16-90 i7'34 15 0-62 0-68 0-62 2'5 °'3 ANTIMONY AND ITS ALLOYS Owing to its brittleness, antimony is rarely used as such, but it forms part of many industrial alloys, such as white bearing metals, type metal, etc. Methods for determining the impurities commonly accompanying com- mercial antimony are therefore described, since the value depends on the purity. Lead-antimony alloys are treated under lead, while alloys of antimony with tin alone or with tin and lead together (white metals) arc dealt with along with tin. ANTIMONY Analysis of commercial antimony is generally limited to the determina- tion of its commoner impurities : lead, bismuth, copper, iron, arsenic and sulphur. 10 grams of the finely powdered sample are treated with aqua regia (140 c.c. HC1, 20 c.c. HN03) diluted with an equal volume of water, the solution thus obtained being treated with 60-70 c.c. of 50% tartaric acid solution, then made alkaline with concentrated sodium hydroxide solution and subjected to a current of hydrogen sulphide. The separation of the sulphides is facilitated by heating on a water-bath, the precipitate being filtered off and washed once or twice with hot water containing a few drops of sodium sulphide. The precipitate is then dissolved in a little hydro- chloric acid containing bromine and 1-2 drops of tartaric acid added to the solution, which is rendered alkaline with sodium hydroxide and again precipitated with hydrogen sulphide to ensure the complete elimination of the antimony. After a short rest on the water-bath, the liquid is filteredtic Determination of Tin in Ordinary Bronzes).